This invention relates to internal combustion engines for propelling motor vehicles. More specifically it relates to improvements in an engine that is equipped with a mechanism for augmenting back-pressure on the engine, and a retarder that, when activated, operates the mechanism to slow the engine by augmenting the engine back-pressure.
A known technique for retarding an internal combustion comprises augmenting engine back-pressure. One way of doing this comprises restricting the exhaust gas flow from the engine. In a conventional camshaft engine, a valve that is disposed in the exhaust system, sometimes called an exhaust brake, can be operated to restrict the exhaust gas flow. In an engine that has variable valve actuation, the individual cylinder exhaust valves may be actuated in a manner that creates the desired restriction.
Certain diesel engines have fuel injection systems that utilize hydraulic fluid under pressure to force fuel into engine combustion chambers. The hydraulic fluid is supplied to a respective fuel injector at each engine cylinder. When a valve mechanism of a fuel injector is operated by an electric signal from an engine control system to inject fuel into the respective cylinder, the hydraulic fluid is allowed to act on a piston in the fuel injector to force a charge of fuel into the respective combustion chamber.
The present invention arises through the recognition that retarding an engine by augmenting exhaust back-pressure inherently creates back forces on the fuel injectors that may cause undesirably high impact loads on the fuel injectors. Over time, the cumulative effect of repeated impacts may accelerate wear and have adverse consequences on performance and durability.
The present invention is directed toward a solution for avoiding such consequences by employing a novel strategy in the engine control system to attenuate the injection control pressure to the fuel injectors in a way that mitigates the effect of augmented back-pressure on the fueling system when the engine retarder is activated to retard the engine. Upon activation of the engine retarder, the strategy attenuates injection control pressure to a defined dwell pressure. Once that dwell pressure has been attained, the strategy keeps the injection control pressure from exceeding the defined dwell pressure. Upon elapse of a dwell time during which the injection control pressure has not exceeded the defined dwell pressure, the strategy increases the hydraulic fluid pressure above the defined dwell pressure.
A timing function sets a predetermined time for the dwell time. During the dwell time, the strategy conditions continued maintenance of the defined dwell pressure upon engine speed not exceeding a speed that, according to a pressure versus speed map, would call for hydraulic fluid pressure to be greater than the defined dwell pressure. Should engine speed begin to exceed a speed that, according to the pressure versus speed map, would call for injection control pressure to be greater than the defined dwell pressure, the strategy discontinues maintenance of the defined dwell pressure and instead increases hydraulic fluid pressure in accordance with the pressure versus speed map.
Upon elapse of the defined dwell time, the strategy increases the injection control pressure as a function of time in accordance with a map of pressure versus time. It also conditions continuation of increasing of the hydraulic fluid pressure in accordance with the pressure versus time map on engine speed not exceeding a speed that, according to the pressure versus speed map, would call for hydraulic fluid pressure to be greater than the hydraulic fluid pressure called for by the pressure versus time map. Should engine speed begin to exceed a speed that, according to the pressure versus speed map, would call for hydraulic fluid pressure to be greater than the hydraulic fluid pressure called for by the pressure versus time map, the strategy discontinues continued increasing of the hydraulic fluid pressure in accordance with the pressure versus time map and instead increases hydraulic fluid pressure in accordance with the pressure versus speed map.
Accordingly, one generic aspect of the present invention relates to an internal combustion engine comprising a fueling system that utilizes hydraulic fluid under pressure to force fuel into engine combustion chambers, an engine control system for controlling various aspects of engine operation including controlling pressure of the hydraulic fluid, and a mechanism for augmenting back-pressure on the engine in response to a command from the engine control system to retard the engine.
In consequence of issuance of the command to retard the engine, the engine control system attenuates the hydraulic fluid pressure to mitigate the effect of augmented back-pressure on the fueling system. Once the hydraulic fluid pressure has been attenuated to a defined dwell pressure, the control system keeps the hydraulic fluid pressure from exceeding the defined dwell pressure. Upon elapse of a dwell time during which the hydraulic fluid pressure has not exceeded the defined dwell pressure, the control system increases the hydraulic fluid pressure above the defined dwell pressure.
Another generic aspect relates to an internal combustion engine comprising a fueling system that utilizes hydraulic fluid under pressure to force fuel into engine combustion chambers, an engine control system for controlling various aspects of engine operation including controlling pressure of the hydraulic fluid, and a mechanism for augmenting back-pressure on the engine in response to a command from the engine control system to retard the engine.
The control system comprises a selector for selecting control of hydraulic fluid pressure from a selected one of plural sources of hydraulic fluid pressure control to the exclusion of other sources of hydraulic fluid pressure control. The one source is selected by a command given in conjunction with the command for the mechanism to retard the engine. In consequence of its selection, the one source controls hydraulic fluid pressure such that the hydraulic fluid pressure is attenuated to, and then kept from exceeding, a defined dwell pressure. After elapse of a dwell time defined by an amount of time during which the actual hydraulic fluid pressure has not exceeded the defined dwell pressure, the one source increases the hydraulic fluid pressure above the defined dwell pressure.
Still another generic aspect relates to a control system for an internal combustion engine comprising a processor for processing various data to develop data for control of various engine functions, including control of hydraulic fluid pressure used by a fueling system to force fuel into engine combustion chambers. Upon the processor developing data calling for actuation of a mechanism for augmenting back-pressure on the engine to retard the engine, the processor executes an algorithm for mitigating the effect of augmented back-pressure on the fueling system by developing data for causing the hydraulic fluid pressure to be attenuated to, and then kept from exceeding, a defined dwell pressure, and after elapse of a dwell time defined an amount of time during which the hydraulic fluid pressure has not exceeded the defined dwell pressure, developing data for causing the hydraulic fluid pressure to increase above the defined dwell pressure.
Still another generic aspect relates to a method for mitigating the effect of augmented back-pressure on an internal combustion engine fueling system that utilizes hydraulic fluid under pressure to force fuel into engine combustion chambers when a mechanism is operated to augment back-pressure on the engine in response to a command from an engine control system to retard the engine. In consequence of issuance of the command to retard the engine, the hydraulic fluid pressure is attenuated to mitigate the effect of augmented back-pressure on the fueling system. Once the hydraulic fluid pressure has been attenuated to a defined dwell pressure, the hydraulic fluid pressure is kept from exceeding the defined dwell pressure. Upon elapse of a dwell time during which the hydraulic fluid pressure has not exceeded the defined dwell pressure, the hydraulic fluid pressure is increased above the defined dwell pressure.